A cyclic-softening macro element model for mono-bucket foundations supporting offshore wind turbines in clay

Abstract

A cyclic-softening macro element model that represents mono-bucket foundation supporting offshore wind turbines in clay is presented in this paper. The model is formulated based on multi-surface plasticity with kinematic and isotropic hardening rule. The softening behaviour of the foundation subjected to a cyclic load sequence is captured real-timely in the macro element model through the contraction of yield surfaces. The model parameters are calibrated by uniaxial quasi-static load–displacement curves, which are obtained by finite element analyses with the cyclic behaviour of soil simulated via the cyclic contour diagram approach. The performance of the macro element model in representing the softening of a bucket foundation during a cyclic load sequence is demonstrated by comparing with parallel finite element analyses. A reasonable agreement has been achieved. The procedure to apply the model is suggested, considering different working scenarios with various cyclic to average load ratios. The macro element model developed is capable of capturing the real-time displacement of foundation in a load sequence, with high computational efficiency and accuracy.